1. Field of Invention
This invention pertains to a method and apparatus for braiding three-dimensional re-enforced fabrics, these types of fabrics are gaining popularity as structural members in the aerospace industry and other industries requiring very light yet durable materials. Composites reinforced with 3-D fabrics exhibit greater isotropy and fracture toughness than those made with conventional cloth or fiber lay-ups.
2. Description of the prior art
The term THREE-DIMENSIONAL FABRIC refers to textile assemblies with interlaced yarns extending into all three dimensions, eliminating non-reinforced planes within a structure. Non-reinforced planes are the weakest segments in a composite structure. Structural faults such as cracking and delamination tend to propagate along these non-reinforced planes.
Three-dimensional braiding devices are disclosed in U.S. Pat. Nos. to Bluck (3,426,804); Florentine (4,312,261) and Brown (4,621,560). The devices disclosed therein have several common characteristics:
1. The zone in which the fabric is formed, hereinafter called the braiding zone, is relatively long in the longitudinal direction;
2. No provision is made to compensate for slack yarns in the braiding zone resulting in movement of the braiding blocks from the perimeter to the center of the braiding matrix.
3. No means are provided for beating or compacting yarn interlacings to form the fabric either within or adjacent to the braiding zone.
In addition, Florentine discloses magnetic means for positioning the braiding elements in a pre-selected orientation, which makes the device expensive and complex. Brown discloses a device which merely provides a means for aligning elements in the braiding plane to prevent jamming during weaving.